Optically Clear Biofouling Resistant Compositions and Methods for Marine Instruments

ABSTRACT

An optically clear biofouling resistant coating compositions specially formulated for very high light transmission and more particularly coating compositions which can be applied to marine instruments and sensors. The compositions provide a biofouling resistant coating on the surface of the marine instruments and sensors which prevents underwater organisms from adhering and growing on the surfaces of the structures over a long period of time.

This invention claims priority to U.S. Provisional Patent ApplicationNo. 61/155,860 filed Feb. 26, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optically clear biofouling resistantcoating organosiloxane compositions specially formulated for very highlight transmission, and more particularly to coating compositions whichcan be applied to marine instruments and sensors. The compositionsprovide a biofouling resistant coating on the surface of the marineinstruments and sensors which prevents underwater organisms fromadhering and growing on the surfaces of the structures over a longperiod of time.

2. Description of the Prior Art

A large number of organisms such as barnacles, bacterial slimes,ascidians, serupulas, fresh- and salt-water mussels, polyzoan, greenalgae, sea lettuce and the like live in the waters of the sea, rivers,lakes and swamps. These plants and animals cause various types ofdamages, and particularly adhere to and degrade the performance ofmarine instruments and sensors.

The biofouling of marine and other aquatic instrumentation is along-felt and well-established problem by those in industry, science andresource management, as biofouling inhibits the performance of marineinstrumentation, thereby adversely affecting the data acquired as wellas adding to the cost of maintaining the instruments. Problems due tobiofouling of marine instrumentation have been occurring for manydecades and continue to be a major factor inhibiting the effective useof submerged instruments.

Biofouling on the marine instrument housing causes messy handling of theinstrument upon retrieval; increases the surface area of the housingthereby making the instrument more susceptible to forces imparted on itfrom current, waves or other moving water; increases the weight of theinstrument both in and out of the water; increases personnel time toclean with an associated increase in operation and maintenance cost thebiofouling that attaches to the surface area of the housing has atendency to migrate towards the sensor area.

Additionally, the biofouling on the sensor elements can attenuate sensorsignals, disrupt critical spacing between conductor elements, disableoptical devices due to blockage of light transmission through theirelements; block open ports of pressure or sensing chambers, clogs openflow cylinders of some sensors and some biofouling organisms such asbarnacles can bore into the transducer elements, thereby damaging them.

Biofouling of marine instruments comprising a housing and sensor elementcontinues to be a persistent problem. Prior attempts to address theproblems associated with biofouling of sensor elements have involvedusing, mechanical wipers to remove biological material from the sensorelements; various grease types which work through ablative processes orthrough the incorporation of active agents such as pepper extracts orother traditional metal biocides, tributyl tin tablets that sterilizethe local sensing area or chamber contained sensor area, usingtraditional paints containing active biocides, sensor encapsulationboxes that prevent light from contacting the sensor element when it isnot in use and thereby prevent or limit biofouling, chlorine systemsthat often use electrolysis to generate chlorines from seawater, variouschemical treatments that are injected into a closed chamber system andusing copper mounting plates for sensor components.

Other prior attempts to address the problems associated with biofoulingof housing elements include the use of various grease types which workthrough ablative processes or through the incorporation of active agentssuch as pepper extracts or other traditional metal biocides, use oftraditional paints containing active biocides, or various types of tapesthat are wrapped on the housings and then removed when the instrument isretrieved, thus removing the biofouling.

Prior art techniques have obvious limitations. For instance, use ofgrease for preventing biofouling of instrument housing may be initiallyeffective; its effectiveness diminishes over time as the greases need tobe periodically reapplied as the grease is washed off. Furthermore,greases may have adverse environmental effects as they are in some casestoxic to non-biofouling marine life and to workers handling andmaintaining the marine instruments. On the other hand, paints or anyopaque coating will not work on optical sensors as they will disruptlight transmission in the same manner that biofouling itself does.Additionally, metal biocide released from various paints or greasescannot work with electrode or electromagnetic sensor elements as theywill disrupt the generated signal. Mechanical wipers have proven toimprove the duration that optical instruments can be deployed. Foulingdoes however occur and the mechanical systems use a significant amountof battery power for those devices that are battery powered.Furthermore, paints containing active biocides or other biocideapplications lose their efficacy over time. The copper mounting platesnoted have moderate effectiveness in reducing biofouling accumulation.The use of tapes on instrument housing does not reduce the degree ofbiofouling but simply protects the instrument housing and allows theuser to clean the instrument by removing the tape rather than scrapingthe instrument.

Where marine instruments have been coated with opaque biofoulingresistant material, the coating occludes the identity of the instrumentcausing manufacturers to loose their identifying look and branding;serial numbers and other identification markings.

In order to solve the above problems, various coating compositions havepreviously been proposed. For example, U.S. Pat. Nos. 4,025,693 and5,218,059, 5,958,116 disclose coating compositions which are preparedusing a silicone rubber alone or as a mixture with silicone oil. US20080166493 disclose silicone based coating compositions containingceramic nanoparticles. US 20080255304 relate to integrally molded bodyof silicone resin and silicone rubber but does not teach anantibiofouling composition. Prior art does not provide optically clearsilicones nor address the issue of poor silicone adhesion to a widevariety of marine instrument surfaces, particularly adhesion promotionin a manner that does not interfere with light transmission. Hence,there is need for biofouling resistant coating compositions speciallyformulated for very high light transmission without impeding theeffectiveness of the submerged instruments.

SUMMARY OF THE INVENTION

The present invention provides an optically clear biofouling resistantorganosiloxane-based coating composition and method for marineinstruments comprising housing and sensor elements, said compositioncapable of forming a coating having excellent biofouling resistantproperties, adhesion to the substrate and coating durability. As used inthis description, instrument housing also includes moveable and fixedplatforms that contain undersea instruments such as Autonomous UnderseaVehicles (AUV), Gliders and Buoys. As used in this specification,optical clarity refers to a coating composition that is opticallytransparent (>70% light transmission between 400 and 800 nm), preferablygreater than 90% light transmission between 400 and 800 nm and mostpreferably greater than 95% light transmission between 400 and 800 nm.Preferably the refractive index of the composition is above 1.40.

The biofouling resistant coating of the invention is the reactionproduct of a composition specially formulated for very high lighttransmission comprising a curably reactive organosiloxane, preferablypolydimethylsiloxane, an organosilane cross linking agent, andoptionally a reinforcing silica or silica resin, where appropriate, ametal catalyst, and where appropriate adhesion promoters, primers andsubstrate surface treatments such as corona.

It is one object of the present invention to provide an optically clearbiofouling resistant coating composition for marine instruments. As usedin this specification, marine instruments encompass instruments intendedto be used in a submerged environment for extended periods of time. Suchinstruments generally comprise a waterproof and pressure proof housingwhich contains a sensor(s) element(s) that is exposed to the ambientwater. The housing typically contains electronics, batteries, datastorage and a means to mount the sensor element. The sensor element istypically an acoustic transducer, optical sensor, electromagneticdevice, electrode device, strain gage device or sensing chamber thatuses any number of chemical, optical or other measurement techniques.

It is another object of the present invention to provide an opticallyclear biofouling resistant coating composition for the waterproofpressure housings of marine instruments, said water proof housings madeof materials including but not limited to aluminum, titanium, stainlesssteel, copper nickel, glass, polyurethane, poly vinyl chloride, ceramic,poly acetyl, fiberglass reinforced plastic, carbon fiber reinforcedplastic, other thermo plastics, other thermo sets.

It is another object of the present invention to provide an opticallyclear biofouling resistant coating composition for the exposed sensorelements of marine instruments; said sensors made of materials includingstainless steel, glass, epoxy, polyurethane, titanium, other thermoplastic plastics, other thermo set plastics, and ceramics.

It is yet another object of the present invention to provide anoptically clear biofouling resistant coating composition for acousticsensors which generally measure ocean current, produce sea bottomimagery, produce mid water imagery, measure small and large aquaticlife, measure suspended sediments or particles in water or produceimagery of man made devises such as ship hulls, mines, shipwrecks andsubmerged structures of various types.

It is yet another object of the present invention to provide anoptically clear biofouling resistant coating composition for opticalsensors which generally measure: dissolved oxygen, florescence,chlorophyll, turbidity, ph and bioluminescence

It is yet another object of the present invention to provide anoptically clear biofouling resistant coating composition for electrodeor electromagnetic sensors which generally measure: conductivity,temperature, and water flow.

It is yet another object of the present invention to provide anoptically clear biofouling resistant coating composition for straingauge devices which generally measure pressure.

The present invention also provides a method of coating marineinstruments comprising housing and sensor elements, said method capableof forming an optically clear biofouling resistant coating havingexcellent biofouling resistant properties, a high degree of coatingadhesion to the substrate as well as a high degree of coatingdurability.

One object of the invention provides a method of coating marineinstruments which generally comprise a waterproof and pressure proofhousing which contains a sensor(s) element(s) that is exposed to theambient water, said method capable of forming an optically clearbiofouling resistant coating having excellent long term biofoulingresistant properties, a high degree of coating adhesion to the substrateas well as a high degree of coating durability.

It is yet another object of the present invention to provide a method ofcoating the waterproof pressure housings of marine instruments, saidwater proof housings made of materials including but not limited toaluminum, titanium, stainless steel, copper nickel, glass, polyurethane,poly vinyl chloride, ceramic, poly acetyl, fiberglass reinforcedplastic, carbon fiber reinforced plastic, other thermo plastics, otherthermo sets, said method capable of forming an optically clearbiofouling resistant coating having excellent biofouling resistantproperties and biofouling resistant durability.

It is another object of the present invention to provide a method ofcoating the exposed sensor elements of marine instruments; said sensorsmade of materials including stainless steel, glass, epoxy, polyurethane,titanium, other thermo plastic plastics, other thermo set plastics, andceramics said method capable of forming an optically clear biofoulingresistant coating having good adhesion to the substrate and coatingdurability.

It is yet another object of the present invention to provide a method ofcoating acoustic sensors, optical sensors, electromagnetic sensors,strain gauge, said method capable of forming an optically clearbiofouling resistant coating having excellent biofouling resistantproperties and biofouling resistant durability.

One embodiment of the invention is one in which the composition andmethod of the present invention is used in conjunction with otherbiofouling resistant methodologies known in the art. For instance, inconjunction with mechanical wiper system, the composition and method ofthe present invention will result in a more effective cleaning of thecoated sensor and/or housing. In another embodiment, the composition ofthe present invention further comprises organic compounds havingantibiofoulant properties selected from compounds consisting ofalgaecides, herbicides, bactericides, and pesticides as well naturalproduct antibiofoulants such as capsaicin and zosteric acid. Mixtures oftwo or more antibiofoulants can be used. Preferred anti biofoulants arethose compounds that are stable at processing conditions and that do notexcessively decrease transmission of light through the cured compositionor damage the compositions' physical and mechanical properties to anyappreciable extent.

In another embodiment, to enhance adhesion of the coating material andincrease biofouling resistant durability, a silicone based primer may beapplied to the sensor or instrument housing to be coated with thecomposition of the present invention. In yet another embodiment, theinstrument housing can be corona treated to promote adhesion of thecoating.

In yet another embodiment, to enhance adhesion of the coating materialand increase biofouling resistant durability, a clear paint barrier suchas epoxy or polyurethane may be applied to the instrument housing orsensor to serve as a tie coat in order to provide barrier substrate forthe composition of the present invention to attach. The barrier willalso prevent any constituents from the instrument housing or sensor fromdisrupting the adhesion of the silicone coating.

The composition of the present invention may be a two part heat-curedsystem or it may be a one part system that is cured at room temperaturesor accelerated temperatures.

The present invention also provides an optically clear biofoulingresistant coating composition and method for marine instrumentscomprising housing and sensor elements, said composition capable offorming a coating having excellent long term biofouling resistantproperties, coating durability and good adhesion to the substrate, saidmethod and composition being environmentally friendly and safe tohandle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates biofouling in o-ring jointed seams of amulti-component marine instrument housing.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be more fully understood by reference to thefollowing description and examples. Variations and modifications of theembodiments of the invention can be substituted without departing fromthe principles of the invention, as will be evident to those skilled inthe art.

The marine instruments which can be coated by the present invention canbe any of the known marine instruments and sensors which are likely tobe used underwater for extended periods of time. These include, forexample, electroacoustic, sonic and optical apparatus for marinepurposes; survey, shipping, signal, measurement and monitoring apparatusfor underwater applications; acoustic echosounders for range measurementin water; temperature, sediment transport, chlorophyll, florescence,turbidity, acoustic fish-finding apparatus, multihydrophone listeningdevices, acoustic locating and control apparatus; apparatus forunderwater telephony; apparatus for pollutant detection and pollutantanalysis in seas and in inland waters; sonar equipments and partsthereof; command and weapons control systems on underwater vessels,mainly consisting of surveillance sensors for sea areas, acoustic homingheads, underwater propelled guided vehicles; underwater locatingapparatus; submerged navigation and control systems for ships;surveillance systems for inland waterways, sea waterways, harbors andcoasts, apparatus for iceberg detection; survey systems for waters andparts of such systems, fanbeam echosounders, underwater recordingapparatus and evaluation apparatus; hydrophone machines and apparatus,namely, hydrophones and underwater recording or listening instruments;underwater surveying apparatus and instruments, namely, surveyingapparatus and instruments in the field of processing, acquisition andinterpretation of seismic data for use in exploration and exploitationof the hydrocarbon deposits in underwater surfaces specifically seismicexploration machines and apparatus; tools with underwater acousticsensors, tools with underwater vibration sensors and tools withunderwater acceleration sensors, namely, seismic exploration machines,seismological instruments, seismometers; underwater scientific apparatusand instruments, namely, scientific apparatus and instruments in thefield of processing, acquisition and interpretation of geophysical datafor use in exploration and exploitation of the aquatic subsoil and forprocessing and interpretation of seismic data for searching out andexploitation of hydrocarbon deposits.

The above marine instruments comprising a housing and sensor elementscan be made of nearly any material which is suitable for theapplication. This includes, for example, plastics, elastomers, metalsand the like. Specific materials for the sensor elements also includebut are not limited to polyvinylchlorides (PVC), polycarbonates (PC),polyurethanes (PU), polypropylenes (PP), polyethylenes (PE), polyesters,polymethylmethacrylate (PMMA), hydroxyethylmethacrylate, N-vinylpyrrolidones, fluorinated polymers such as polytetrafluoroethylene,polyamides, polystyrenes, copolymers or mixtures of the above polymers.

The marine instrument made of the above materials is coated with theoptically clear biofouling resistant coating of the invention. As usedin this description, “biofouling resistant,” “fouling release,” or“antibiofouling” are used interchangeably to refer to the process ofpreventing or reducing the accumulation of fouling organism on marineinstrument housing and sensor elements using the methods and compositionof the present invention. The entire device may be coated with thiscoating or, alternatively, just that portion of the device that issubmerged under water can be coated. It is understood by one of skill inthe art that the different embodiments of a particular marine instrumentmay be coated with different biofouling resistant coating compositionsmost suited for its constituent materials.

The biofouling resistant coating of the invention is the reactionproduct of a composition specially formulated for very high lighttransmission comprising a curably reactive organopolysiloxane havingreactive functional groups and silicon bonded organic groups, a crosslinking agent, optionally a filler or a reinforcing silica, optionallyan adhesion promoter, and optionally a metal catalyst. Preferred siliconbonded organic group include a methyl group, an ethyl group, a vinylgroup, a haloalkyl group, and a phenyl group. The specific curingmechanism can vary widely, and depends on the nature of the functionalgroups, for example, hydrolyzation, dealcoholyzation, deacetification,dehydroxyamination and the like. In a preferred embodiment, at least oneterminal end of the organopolysiloxane polymer has at a terminalreactive group; preferably the terminal reactive group is a hydroxylgroup, an alkoxy group, an aryloxy group, an amino group, an amidogroup, a halogen, or a vinyl group.

The curably reactive organopolysiloxane is preferably a reactivepolydimethylsiloxane (PDMS) (H₃C)₃SiO[Si(CH₃)₂O]_(n)Si(CH₃)₃, where n isthe number of repeating monomer [SiO(CH₃)₂] units, said reactive PDMSbeing preferably condensation or addition/heat cured.

Condensation cured materials are room temperature vulcanizing resins(RTVs) which use ambient moisture for curing. Condensation cures canalso be of the neutral type that can be cured by either alkoxy or oxinepromoter released from the material. They can be commercially availableas one part systems. Condensation cured materials can also be two partsystems. These use what is typically a metal catalyst in conjunctionwith the ambient moisture. These materials are not susceptible topremature curing by exposure to moisture. These material types aretypically alkoxy cross link promoter released. Addition cure materialsuse platinum as the catalyst. They are designed to be heat curedmaterials but are sometimes reformulated to cure at room temperatures.This type of material has no by products. Addition cure materials tendto have better optical clarity than condensation curedorganopolysiloxane. As used in this specification, optically clearcoating refers to fouling release coating of the present inventionhaving a high refractive index and light transmission of greater than50%.

In one embodiment, the reactive organopolysiloxane can be nearly anywhich reacts with acetoxysilane cross linking agent to cure and form theoptically clear biofouling resistant coating. Such organopolysiloxanesgenerally have reactive groups such as hydrogen, hydroxyl, alkoxy oralkoxy bound to silicon in the polymer. As such, the reactiveorganopolysiloxanes generally have siloxane units of the generalstructure:

R_(x)R¹SiO_((3-x))  I

in which each R represents a monovalent hydrocarbon group having up to20 carbon atoms such as an alkyl (e.g., methyl, ethyl, propyl or butyl)or phenyl groups, x is 1 or 2 and R¹ represents a hydrogen, a hydroxyl(OH) group or an alkoxy group (OR) such as methoxy, ethoxy, propenyloxyand the like. Preferably, R is methyl and R¹ is hydroxyl.

The reactive organopolysiloxanes can, and preferably does, also haveother units such as, for example, units of the general structure:

R_(y)R¹SiO_((4-y))  II

in which R is as above, and y is 0, 1, 2 or 3. In addition, oralternatively, the organopolysiloxane can also contain, for example,organic groups such as acrylates, carbonates, polybutylenes or the like.

The reactive organopolysiloxane can also comprise mixtures or copolymersof the above organopolysiloxanes. Obviously, however, theorganopolysiloxane must have at least one, preferably at least two,units of formula I for cross linking.

In a preferred embodiment of the invention, the reactiveorganopolysiloxane comprises a organopolysiloxane having the structure.

OH(Si(CH₃)₂))_(z)H  III

wherein z is an integer of 3 to 10,000 or more.

The reactive organopolysiloxanes can have a wide variety of viscositiessuch as from about 10,000 cps and 400,000 cps at 25° C.

The acetoxysilane cross linking agent of the reactive organopolysiloxaneof formula I comprises a material or a mixture of materials of thestructure

R² _(4-a)SiR³a

in which R² is a monovalent hydrocarbon group having up to 20 carbonatoms such as an alkyl (e.g., methyl, ethyl, propyl or butyl) or aphenyl group, R³ is an acetoxy group, and a is 2, 3, or 4. In addition,the hydrolysis and condensation products of these silanes such as, forexample, organopolysiloxanes containing the above acetoxy groups arealso functional herein. Examples of specific acetoxysilanes includemethyltriacetoxysilane, ethyltriacetoxysilane and mixtures thereof. Theacetoxy cross linking agents are used in amounts of about 10 ppm to 10wt % based on the weight of the organopolysiloxane. Preferably, theamount of cross linking agent is sufficient to provide a ratio ofreactive groups on the organopolysiloxane to acetoxy groups of 0.1 to 10and more preferably 0.5 to 2.

The metal catalysts suitable for use in the acetoxy curing reactiveorganopolysiloxane are known in the art and may include, for example,organic metal compounds such as organotin salts. Examples of catalystsinclude stannous octoate, dibutyltin dilaurate, dibutyltin diacetate,dimethyltin dineodecanoate, dibutyltin dimethoxide, isobutyl tintriceroate, dimethyltin dibutyrate, dimethyltin dineodecanoate,triethyltin tartrate, tin oleate, tin naphthenate, tin butyrate, tinacetate, tin benzoate, tin sebacate, and tin succinate, platinum.Generally, these catalysts are used in amounts of between about 0.001and 10 wt. % based on the weight of the composition. Platinum catalystis preferred for the optically clear biofouling resistant compositionsof the present invention specially formulated for very high lighttransmission.

In another embodiment, the curably reactive organopolysiloxane is apolydimethylsiloxane capped at both molecular terminals withdimethylvinylsiloxy groups, a methylvinylsiloxane.dimethylsiloxanecopolymer capped at both molecular terminals with trimethylsiloxygroups, a methylvinylsiloxane.dimethylsiloxane copolymer capped at bothmolecular terminals with dimethylvinylsiloxy groups, amethylvinylsiloxane.dimethylsiloxane copolymer capped at both molecularterminals with dimethylvinylsiloxy groups, amethyl(3,3,3-trifluoropropyl)siloxane.dimethylsiloxane copolymer cappedat both molecular terminals with dimethylvinylsiloxy groups, apolydimethylsiloxane capped at both molecular terminals withdimethylhexenylsiloxy groups, a methylhexenylsiloxane.dimethylsiloxanecopolymer capped at both molecular terminals with trimethylsiloxygroups, a methylhexenylsiloxane.dimethylsiloxane copolymer capped atboth molecular terminals with dimethylhexenylsiloxy groups, amethylphenylsiloxane.dimethylsiloxane copolymer capped at both molecularterminals with dimethylhexenylsiloxy groups, and amethyl(3,3,3-trifluoropropyl)siloxane.dimethylsiloxane copolymer cappedat both molecular terminals with dimethylhexenylsiloxy groups.

A preferred cross linking agent is a polyorganosiloxane that contains atleast two silicon-bonded hydrogen atoms in its molecule and can berepresented by methyl, ethyl, propyl, and other alkyl groups; phenyl,tolyl, and other aryl groups; phenethyl or other univalent hydrocarbongroups represented by aralkyl groups; 3-chloropropyl group,3,3,3-trifluoropropyl group, and other halogenated alkyl groups.Preferably, the cross linking agent is a polymethylhydrogensiloxanecapped at both molecular terminals with trimethylsiloxy groups, amethylhydrogensiloxane.dimethylsiloxane copolymer capped at bothmolecular terminals with trimethylsiloxy groups, a cyclicmethylhydrogensiloxane.dimethylsiloxane copolymer capped at bothmolecular terminals with dimethylhydrogensiloxy groups, amethylhydrogensiloxane.dimethylsiloxane copolymer, cyclicpolymethylhydrogensiloxane, an organosiloxane copolymer consisting ofsiloxane units R₃SiO₁/2, siloxane units R₂HSiO₁/2, and siloxane unitsSiO₄/2, an organosiloxane copolymer consisting of siloxane unitsR₂HSiO₁/2 and siloxane units SiO₄/2, an organosiloxane copolymerconsisting of siloxane units of formula RHSiO₂/2 and siloxane units offormula RSiO₃/2 or siloxane units of formula HSiO₃/2, or a mixture oftwo or more of these polyorganosiloxanes. R is a univalent saturatedhydrocarbon group or a halogenated alkyl group. Preferably, the amountof cross linking agent is sufficient to provide a ratio of reactivegroups on the organopolysiloxane to hydrogen atoms on the cross linkingagent of 0.1 to 10 and more preferably 0.5 to 2.

In a preferred embodiment, the curably reactive organopolysiloxane is avinyl-terminated PDMS, which can be synthesized by the reaction ofcommercial hydroxyl-terminated PDMS with dimethylvinylchlorosilane toyield compounds of the following chemical formula

The vinyl groups in the above PDMS polymer can copolymerize withvinyltrialkyloxysilane, and can also take part in a cross-linkingreaction with 1,3-divinyltetramethyldisiloxane.

The fouling resistant composition of the present invention may alsocomprise rheological control and reinforcing fillers. Such fillers areknown in the art and generally comprise those conventionally found insilicone elastomers. They include, for example, precipitated or fumedsilicas which may be pre-treated or treated in situ to render themhydrophobic. These control viscosity, thixotropy, flow, sag resistance,and sedimentation and have surfaces comprising siloxane and silanolfunctionalities. The viscosity of the silicone resin is preferablyadjusted such that a uniform coating results with a thickness of between2/1000 and 10/10000 of an inch.

Preferably, for the optically clear biofouling resistant compositions ofthe present invention specially formulated for very high lighttransmission, the filler comprises nanoparticles of amorphous fumedsilica having a primary particle size between 5 to 150 nanometer (nm)with 50-800 m²/g surface area, preferably 120-200 m²/g, untreated ortreated with silanes (e.g. trimethylchlorosilane), silazane (e.g.hexamethyldisilazane) or low molecular weight organopolysiloxane such asorganoalkoxysilane, organochlorosilane, organosilazane, or other organicsilicon compound and mixtures thereof. In dimethylsiloxane,dimethylyvinyl-terminated anti fouling compositions, dimethylyvinylatedand trimethylated silica may be used. In dimethylsiloxane, hydroxylterminated anti fouling compositions, untreated amorphous fumed silicamay be used.

Examples of fumed silica (modified or unmodified) include, but are notlimited to, Bindizil® 215 (anionic surface), Bindizil® 15/500 (anionicsurface), Bindizil® 30/360 (anionic surface), Bindizil® 830 (anionicsurface), Bindizil® 2034 DI (anionic, acid surface), Bindizil® 9950(anionic surface), Bindizil® 50/80 (anionic surface), Bindizil® CAT80(cationic surface), Bindizil® CC30 (silane treated surface) andCabosil®. Preferably, hydrophobic fumed silica is used by treating thesurface of hydrophilic fumed silica such as Aerosil® to render it waterrepellent. Degussa's Aerosil® P202 is treated with polymethylsiloxane(silicone oil) and Aerosil® R805 is treated with trimethoxyoctylsilane.

Generally, more dispersing energy is needed to disperse a given amountof silica as the surface area increases. In other words, silicas withlower surface area are easier to disperse. In a fully dispersed system,lower surface area silicas require a higher weight loading in the resinthan those of higher surface area to achieve similar viscosities andbehaviors. Viscosity can be measured by use of commonly availableviscometers.

The fillers are used in an amount sufficient to provide the desiredproperties. Generally, this is an amount of about 0.1 to 70 parts perhundred parts of the organopolysiloxane, preferably ranging from about 5wt % to about 70 wt % of the organopolysiloxane or about 7 wt % to about35 wt % or about 7 wt % to about 15.0 wt % or about 30 wt % to about 60wt %. The amount added depends on the resin chemistry and molecularweight distribution, dispersion condition (intensity, equipment) andnature of other additives used in formulating the antibiofoulingcomposition.

Particle size distributions of the amorphous fumed silica nanoparticlesmay fall anywhere within the range from about 1 nm, or less, to lessthan about 400 nm, alternatively from about 2 nm to less than about 300nm, alternatively from about 5 nm to less than about 150 nm,alternatively 1 nm to 100 nm, alternatively 5 nm and 50 nm,alternatively 1 nm and 25 nm, and alternatively 1 nm and 10 nm.

Fumed silicas should be incorporated based on individual formulationneeds and experience. Typical application methods suggest that thesilica can be incorporated early into the base resin to increase theviscosity of the system. This increase in viscosity results in anincrease of the shear forces that are needed for proper dispersion ofthe silica into the formulation. In many cases, the mixture is sheareduntil a specific, desired “grind”—as an indication of the extent ofdispersion—is achieved. At this point, the other additives, as well asany required reactive diluent, can be added. The actual method ofincorporation may vary depending on the specific formulation, dispersingequipment, and customer specificity. Grindometer readings of <50 μm aregenerally preferred, which indicates nearly complete dispersion.Grindometer readings of 15-40 μm will give best anti-settling, anti-sag,clarity, and stability.

In order to boost the strength, viscosity and improve the long-termstability of antibiofouling coating compositions, additives at aconcentration of 7-30% by weight of fumed silica may be added. Suchadditives can comprise glycols and non-ionic surfactants of variousmolecular weights, which can range from simple ethylene glycol to largerpropylene glycols with molecular weights of 750. The actual materialsand the amounts used are a function of both formulation and customerspecifications. The mechanism by which the additives function depends onthe particular material used. Glycerin, glycol, and other polyhydroxylcompounds have multiple hydrogen bonding sites which allow them to actas “bridging agents” between fumed silica aggregates. This bridgingstrengthens the silica network, resulting in increased viscosity.

In another embodiment, resin fillers in addition to fumed silica or inlieu of fumed silica may be used for material strength and rheologicalcontrol. Resin fillers are short chain silicone polymers such as shortchain polymethylsilsesquioxane that are soluble in the fouling releasesilicone composition itself. They have the best optical properties butat the sacrifice of the final silicone's products strength anddurability.

The biofouling resistant coating of the present invention may contain acuring catalyst in an amount sufficient for cross-linking and curing.

In one embodiment, the curing catalyst comprises organic peroxides suchas 2,5 dimethyl-2.5 di(t-butylperoxy) hexane, 2,4 dichloro-benzoylperoxide, or dicumyl peroxide for peroxide initiated cure.

Preferably, a platinum group metal catalyst such as ruthenium, rhodium,palladium, osmium, iridium, or platinum per se, or compounds of thesemetals that possess a catalytic activity with regard to the curingreaction, such as platinum on a fine-powdered silica carrier,chloroplatinic acid, an alcohol solution of a chloroplatinic acid, aplatinum-olefin complex, a divinyl-tetramethyldisiloxane complex of achloroplatinic acid, a divinyl-tetramethyldisiloxane complex ofplatinum, and thermoplastic resin powders that contain platinum-groupmetals. Preferably, the catalyst should be used in a catalytic amount. Apreferred catalytic amount is 0.1 to 1,000 ppm of the pure metalcontained the catalyst per total amount of curably reactiveorganopolysiloxane.

If desired, the antibiofouling composition of the present invention maycontain additional optically clear ingredients such as diluents,extenders, for example silicone fluids, silicone resins, stabilizers, orsurfactants, biocides, and processing aids such as cyclic or linearpolydiorganosiloxanes. One embodiment comprising dimethylsiloxane,dimethylvinyl terminated based antibiofouling composition, furthercomprises up to 35 wt % vinyl containing resin (polyalkylakenylsiloxane)Vi[CH₃)₂SiO]n Si(CH₃)₂Vi.

One particularly advantageous optional ingredient in the formulation ofthe present invention is a diluent. Such diluents are often necessary todecrease the viscosity of the silicones sufficiently to permitapplication.

Examples of diluents include silicon containing materials such ashexamethyldisiloxane, octamethyltrisiloxane, and other short chainlinear siloxanes, cyclic siloxanes such as octamethylcyclotetrasiloxaneand decamethylcyclopentasiloxane, organic materials such as alkanes andalkenes, including ethylbenzene, xylene, benzene, toluene, alcohol,mineral spirit, acetone, tetrahydrofuran, methylethylketone,methylisobutylketone or any other material or mixture of materials whichcan dilute the formulation without affecting any of the components ofthe formulation.

One embodiment of the antibiofouling coating composition of the presentinvention comprises 40-70 Wt % dimethyl, methylhydrogen siloxane; 15-40%dimethyl siloxane, dimethylvinyl-terminated; 10-30 wt %dimethylvinylated and trimethylated silica; 1.0-5.0 tetramethyltetravinyl cyclotetrasiloxane; less than 1 wt % ethylbenzene, 0.5 wt %xylene, and a catalytic amount of platinum.

Another embodiment of the antibiofouling coating composition of thepresent invention comprises 60-90 wt % vinylpolydimenthylsiloxane;10-30% vinyl containing resin (ployalkylalkenylsiloxane); 0.0001benzene; 0.0001 toluene and a catalytic amount of platinum.

Another embodiment of the antibiofouling coating composition of thepresent invention comprises about 60-80 wt % dimethylsiloxane,hydroxy-terminated; 7.0-13.0 wt % amorphous fumed silica; 1.0-5.0 wt %ethyltriacetoxysilane; 1.0-5.0 wt % methyltriacetoxysilane. Suitableadditives for this embodiment include at least one oftetramethoxysilane, tetraethoxysilane, dimethyldimethoxysilane,methylphenyldimethoxysilane, methylphenyldiethoxysilane,phenyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane,vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, orother alkoxysilanes.

To improve the adhesive properties of the antibiofouling composition,the composition may be combined with an adhesion promoter. Adhesionpromoter is exemplified by silane coupling agents such as3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyl trimethoxysilane,or similar organoalkoxysilanes that contains an acryloxy group;3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)-aminopropyltrimethoxysilane, or similar organoalkoxysilanes that contains an aminogroup; 3-glycidoxypropyltrimethoxysilane, similar organoalkoxysilanesthat contains an epoxy group, or condensation-reaction products such asa condensation reaction product between 3-glycidoxypropyltrialkoxysilaneand a silanol-endcapped dimethyloligosiloxane, a condensation reactionproduct between 3-glycidoxypropyltrialkoxysilane and a silanol-endcappedmethylvinyloligosiloxane, and a product of a condensation reactionbetween 3-glycidoxypropyltrialkoxysilane and a silanol-endcappeddimethylsiloxane-methylvinylsiloxane copolymer and mixtures thereof. Theadhesion promoters can be used in an amount of 0.1 to 10 parts byweight, preferably 0.1 to 5 parts by weight, per 100 parts by weight ofthe sum of the PDMS resin.

In another embodiment, the adhesion promoter may contain a mixture oforganic and inorganic compounds. Dow Corning DC5200 for instancecomprises 60.0-85 wt % Octamethyltrisiloxane, 5.0-10.0 wt %1-Methoxyisopropyl orthosilicate, 5.0-10.0 Tetrapropyl orthosilicate,and 3.0-7.0 Tetrabutyl titanate.

In another embodiment, a primer or tie coat polymer capable of formingan intimate covalent bond matrix with the instrument housing and/orsensor surface is applied prior to applying the PDMS basedantibiofouling coating composition of the present invention. Commercialavailable tie coat resins may be used. U.S. Pat. No. 5,449,553 and U.S.Pat. No. 5,593,732, US Published Application No. 20080138634 disclosetie coat composition and are herein incorporated by reference. Suitabletie coats may have viscosity of from about 400 to about 400,000centipoise at about 25° C.; preferably about 100,000 to about 300,000centipoise at 25° C.; and more preferably, about 95,000 to about 150,000centipoise at 25° C.

In one embodiment, the tie coat is bonded to the substrate and the PDMSoptically clear fouling release coating of the present invention throughsilicone cross linking between the tie coat and fouling release coat.This bond is covalent in nature and results in a transmission oftoughness to the fouling release coat from the tie coat and allows theentire system to achieve a very strong toughness. Commercially availablesilicone based tie coats include SS4179 (GE/MOMENTIVE), SS4044(GE/MOMENTIVE), SS4004 (GE/MOMENTIVE). As used in this description, tiecoat encompasses primers, epoxy resins, and barrier coats or anypre-antifoulant coat layer.

In another embodiment, a clear epoxy adhesive is first applied to thesubstrate optionally followed by a tie coat layer prior to applying thePDMS based antibiofouling composition of the present invention. Theepoxy adhesive preferably comprises a polymer blend containing silanecoupling agent having primary or secondary amines and adheres stronglyto both similar and dissimilar materials including metals, glass,ceramics, vulcanized rubbers and many plastics. One preferred epoxyresin is a polyamine/polyamide blend comprising 65-70 Wt % Bisphenola-epichlorohydrin polymer; 30-35 wt % Alkyl(c12-14) glycidyl ether;diluent n-Butyl glycidyl ether; and fatty acids, C18-unsatd., dimers,reaction products with polyethylenepolyamines (Polyamide Resin) Anotherpreferred epoxy resin comprises Polyoxypropylenediamine 25-50%; Reactionproducts of isophorone diamine with phenol/formaldehyde 10-25%;Isophoronediamine 10-25%; Reaction products of benzene-1,3-dimethanaminewith hydroxybenzene and formaldehyde 10-25%; Hydroxybenzene 5-12% andm-Xylene diamine 5-12%. And yet another preferred epoxy resin comprisesBisphenol-A type epoxy resin 50-70%; Benzyl alcohol 10-20% Bisphenol-Ftype epoxy resin 10-20%; Ethylene glycol monobutyl ether 0.1-0.3% U.S.Pat. No. 6,391,464, entitled Epoxy Coatings and Surfaces CoatedTherewith disclose other epoxy coating compositions and is hereinincorporated by reference.

In another embodiment, the barrier coat or tie coat preferably comprisespolyurethane adhesives or other suitable barrier coats used in the art.The adhesives suitable according to the invention are one-componentpolyurethane adhesives or two-component polyurethane adhesives. Theadhesives may be liquid, but they may also be hot-melt adhesives. Theadhesives may contain solvent, but they are preferably solvent-free.Crosslinking of the polyurethane adhesives suitable according to theinvention is based on the reaction of reactive NCO groups, in particulararomatic NCO groups, with H-acidic functional groups, for example OHgroups, amino groups or carboxyl groups. An alternative crosslinkingmethod involves the reaction of the NCO groups with moisture from theapplied adhesive, the substrate or the surroundings with formation ofurea groups. These crosslinking reactions are known and they may alsoproceed concurrently. The adhesives conventionally contain catalysts,for example amine or tin catalysts, to accelerate such reactions.

Known coating material or adhesive polyisocyanates may be used such aspolyisocyanates having two or more isocyanate groups. Suitablepolyisocyanates are for example 1,5-naphthylene diisocyanate (NDI), 2,4-or 4,4′-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H12MDI),xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI),di- and tetraalkylene diphenylmethane diisocyanate, 4,4′-dibenzyldiisocyanate, 1,3- or 1,4-phenylene diisocyanate, tolylene diisocyanate(TDI), 1-methyl-2,4-diisocyanatocyclohexane,1,6-diisocyanato-2,2,4-trimethylhexane,1,6-diisocyanato-2,4,4-trimethylhexane,1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI),tetramethoxybutane 1,4-diisocyanate, butane 1,4-diisocyanate, hexane1,6-diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane1,4-diisocyanate, ethylene diisocyanate, methylene triphenyltriisocyanate (MIT), phthalic acid bis-isocyanatoethyl ester,trimethylhexamethylene diisocyanate, 1,4-diisocyanatobutane,1,12-diisocyanatododecane and dimer fatty acid diisocyanate.

Suitable at least trifunctional isocyanates are polyisocyanates whichare obtained by trimerization or oligomerization of diisocyanates or byreaction of diisocyanates with low molecular weight polyfunctionalcompounds containing hydroxyl or amino groups. Commercially obtainableexamples are trimerization products of the isocyanates HDI, MDI or IPDIor adducts of diisocyanates and low molecular weight triols, such astrimethylolpropane or glycerol.

In another embodiment, silane-functional polyurethanes may be used asmoisture-curing adhesives and sealants. These silane-functionalpolyurethanes contain silane groups as reactive groups and are typicallyprepared by the reaction of aminosilanes with polyurethane prepolymerscontaining isocyanate groups. EP-A-0 202 491 mentionssilane-functionalized polyester melt adhesives in which an adduct of apolyester polyol and a diisocyanate is reacted with an amino- ormercaptosilane, or an adduct of an amino- or mercaptosilane and adiisocyanate is reacted with a polyester polyol. EP-A-0 371 370discloses melt adhesives which after crosslink on exposure to moistureand contain terminal alkoxysilane and/or NCO groups. EP-A-0 371 370further discloses that these alkoxysilane end groups can be introducedvia mercaptosilane or via a series of aminosilanes.

It is conventional to use low molecular weight isocyanates in thesynthesis of polyurethane adhesives. For chemical reasons, it isimpossible to prevent small proportions of monomeric isocyanates fromalso being present in the adhesive. In a further group of polyurethaneadhesives, oligomeric isocyanates are added to the adhesive to improvespecific characteristics. These are intended to react with crosslinkingagents, for example polyols, or with water, in order to yield acrosslinked adhesive.

Prior to applying the tie coat or epoxy resin, all bonding surfaces arecarefully cleaned, degreased and dried to obtain maximum bond strength.Also, when bonding to certain metal surfaces, vulcanized rubbers, etc.,chemical etching may be employed for optimal adhesion and environmentaldurability. Non-porous surfaces may be roughened with sandpaper or emerypaper for hard materials. Where appropriate, air plasma or coronatreatment is applied to the surface to be coated to improve thecharacteristics of the materials by raising surface energy (dyne level).Commercially available corona treatment equipments may be used.

Mixing of the components of the invention causes curing in the presenceof adequate moisture or heat. As such, the components are often storedin separate containers prior to use or they are mixed and stored incontainers which exclude moisture. For instance, one container couldcontain the catalyst and a second could contain the reactiveorganopolysiloxane and the cross linking agent. Alternatively, thecatalyst could be mixed with the reactive organopolysiloxane in onecontainer and the cross linking agent could be in a second container.The filler and optional ingredients could be included in either or bothof the parts depending on factors such as stability, viscosity, andinteractions.

Curable bioresistant composition is prepared by uniformly mixing thecurably reactive organopolysiloxane and the cross linking agent withaddition of other optional components. The composition can be preparedin a commercial mixer such as a Ross mixer, planetary mixer, or Hobartmixer.

The composition of the present invention is then mixed and applied tothe marine instrument housing and sensor elements. The method ofapplying can be, but is not limited to, dip coating, spray coating orflow coating. For example, they can be deposited via anelectrodeposition technique such as electroplating, electrophoreticdeposition, or electrobrushing.

The diluent, if used, is then allowed to evaporate leaving the curedcomposition. If desired, the coated device can be heated or radiated tofacilitate the cure. Heating can be at temperatures of 50° C. to 120° C.for several minutes up to several hours, depending on the heat stabilityof the substrate.

The resultant device has a thin, adherent silicone coating which rendersit biofouling resistant. The coating can have a variety of thicknessessuch as from about several nanometers up to several millimeters,preferably 2/1000 to 10/10000 of an inch.

In order that the invention may become more clear there now followsexamples which are illustrative of the invention. Unless indicated, allparts are by weight and all viscosities are at 25° C.

One embodiment of the invention is one in which the composition andmethod of the present invention is used in conjunction with otherbiofouling resistant methodologies known in the art. For instance, inconjunction with mechanical wiper system, the composition and method ofthe present invention will result in a more effective cleaning of thecoated sensor and/or housing. In another embodiment, the composition ofthe present invention further comprises organic compounds havingantibiofoulant properties selected from compounds consisting ofalgaecides, herbicides, bactericides, and pesticides as well naturalproduct antibiofoulants such as capsaicin and zosteric acid. Mixtures oftwo or more antibiofoulants can be used.

Preferred anti foulants are those compounds that are stable atprocessing conditions and that do not excessively decrease transmissionof light through the cured composition or damage the compositions'physical and mechanical properties. It is anticipated that theantibiofoulants will diffuse over time to the surface of a coatingcomposition and leach out of the coat. Diffusion through the biofoulingresistant coating will provide a long-lived protective coating.

The anti fouling agents must be chosen and incorporated so that they donot excessively decrease transmission of light through theorganopolysiloxane polymer. This normally means that they must form asolid solution in the polymer, as opposed to a suspension. Commonanti-biofoulants include, but are not limited to algaecides, herbicides,bactericides, and pesticides. These materials may be synthesized (e.g.urea-based algaecides, glyphosates (herbicide), fluoroquinolones(bactericide), copper oxides, etc.), or they may be naturally occurring(e.g., capsaicin, zosteric acid, etc.). The antibiofoulants must bestable at the processing conditions of the polymer. Preferredantibiofoulants are not expected to form bound complexes with thecoating composition. The final product preferably has opticaltransparency greater than 70%, good adhesion, the ability to inhibitbiological fouling, and a low leach rate of the antibiofoulants into theenvironment.

Transmission spectra may be determined in any suitable manner in the artsuch as by the use of a UV-Visible spectrometer using a 600 groove/mmgrating with a 300 nm blaze wavelength and 25 μm slit. The “percenttransmission” or amount of light allowed to pass through the polymersamples over a spectral range of 400 to 850 nm is determined. 100%transmission is effectively passing all of the tested wavelengths oflight through the sample. Preferably, the optically clear antibiofoulingcomposition of the present invention has an index of refraction above1.40, most preferably within the range of 1.45 to 1.56 at 25° C.

Example 1

For the case of instrument housings, gliders and similar platforms,special care is taken to coat the areas where sections of housing arejoined together with o-ring connections or have installed end caps witho-ring sections. FIG. 1 illustrates biofouling in o-ring jointed seams10 of multi-component instrument housing 20. In order to protect theseareas from biofouling settlement and to ensure that the applied foulingrelease coating does not flow into the o-ring sealed area where it coulddisrupt the sealing mechanism, the following method of coating isimplemented. A layer of clear plastic tape is applied to cover theo-ring bearing seams joining two pieces of the instrument housing. Toequalize the pressure across the tape, a hole or holes is made on thetape. The anti-fouling coating is then applied over the tape inaccordance with the teachings of the present invention. The circularcircumference, joining two pieces of the instrument housing as describedhave a layer of clear plastic tape applied. The coating is then appliedover the tape.

While the disclosure has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims. Documents including patents and non patent referencescited herein are expressly incorporated by reference.

1. An optically clear biofouling resistant organosiloxane-based coatingcomposition for marine instrument housings and sensors comprisingcurably reactive organopolysiloxane having at least one terminalreactive functional group and silicon bonded organic groups, anorganopolysiloxane cross linking agent, optionally a filler and/or areinforcing silica, optionally an adhesion promoter, and optionally ametal catalyst; wherein said terminal reactive group is a hydroxylgroup, an alkoxy group, an aryloxy group, an amino group, an amidogroup, a halogen, or a vinyl group; and said silicon bonded organicgroup is a methyl group, an ethyl group, a vinyl group, a haloalkylgroup, or a phenyl group.
 2. The optically clear biofouling resistantorganosiloxane-based coating composition for marine instrument housingsand sensors of claim 1, wherein the curably reactive organopolysiloxaneis a hydroxyl, alkoxy, aryloxy, amino, amido, halogen, or vinyl groupterminated polydimethylsiloxane.
 3. The optically clear biofoulingresistant organosiloxane-based coating composition for marine instrumenthousings and sensors of claim 1, wherein the filler comprisesnanoparticles of amorphous fumed silica untreated or treated withsilanes.
 4. The optically clear biofouling resistantorganosiloxane-based coating composition for marine instrument housingsand sensors of claim 3, wherein said amorphous fumed silica is treatedwith trimethylchlorosilane, hexamethyldisilazane, or low molecularweight organoalkoxysilane, organochlorosilane, organosilazane.
 5. Theoptically clear biofouling resistant organosiloxane-based coatingcomposition for marine instrument housings and sensors of claim 1,wherein the filler is a resin filler comprising short chain siliconepolymers that are soluble in the biofouling resistantorganosiloxane-based coating composition.
 6. The optically clearbiofouling resistant organosiloxane-based coating composition for marineinstrument housings and sensors of claim 1, wherein the catalyst iscatalytic amount of a platinum group metal catalyst.
 7. The opticallyclear biofouling resistant organosiloxane-based coating composition formarine instrument housings and sensors of claim 1, further comprisingoptically clear ingredients such as diluents, extenders, stabilizers,surfactants, and processing aids such as cyclic or linearpolydiorganosiloxanes.
 8. The optically clear biofouling resistantorganosiloxane-based coating composition for marine instrument housingsand sensors of claim 7, wherein the diluents include silicon short chainlinear siloxanes, cyclic siloxanes, and organic solvents.
 9. Theoptically clear biofouling resistant organosiloxane-based coatingcomposition for marine instrument housings and sensors of claim 1,comprising about 40-70 wt % dimethyl, methylhydrogen siloxane; 15-40%dimethyl siloxane, dimethylvinyl-terminated; 10-30 wt %dimethylvinylated and trimethylated silica; 1.0-5.0 tetramethyltetravinyl cyclotetrasiloxane; less than 1 wt % ethylbenzene, 0.5 wt %xylene, and a catalytic amount of platinum.
 10. The optically clearbiofouling resistant organosiloxane-based coating composition for marineinstrument housings and sensors of claim 1, comprising about 60-90 wt %vinylpolydimenthylsiloxane; 10-30% vinyl containing resin(ployalkylalkenylsiloxane); 0.0001 benzene; 0.0001 toluene and acatalytic amount of platinum.
 11. The optically clear biofoulingresistant organosiloxane-based coating composition for marine instrumenthousings and sensors of claim 1, comprising about than 60-80 wt %dimethylsiloxane, hydroxy-terminated; 7.0-13.0 wt % amorphous fumedsilica; 1.0-5.0 wt % ethyltriacetoxysilane; 1.0-5.0 wt %methyltriacetoxysilane.
 12. The optically clear biofouling resistantorganosiloxane-based coating composition for marine instrument housingsand sensors of claim 11, further comprising at least one oftetramethoxysilane, tetraethoxysilane, dimethyldimethoxysilane,methylphenyldimethoxysilane, methylphenyldiethoxysilane,phenyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane,vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, orother alkoxysilanes.
 13. The optically clear biofouling resistantorganosiloxane-based coating composition for marine instrument housingsand sensors of claim 1, wherein the adhesion promoter is at least onesilane coupling agent selected from the group consisting of3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyl trimethoxysilane,3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, a condensationreaction product between 3-glycidoxypropyltrialkoxysilane and asilanol-endcapped dimethyloligosiloxane, a condensation reaction productbetween 3-glycidoxypropyltrialkoxysilane and a silanol-endcappedmethylvinyloligosiloxane, condensation reaction product between3-glycidoxypropyltrialkoxysilane and a silanol-endcappeddimethylsiloxane-methylvinylsiloxane copolymer.
 14. The optically clearbiofouling resistant organosiloxane-based coating composition for marineinstrument housings and sensors of claim 1, wherein the adhesionpromoter comprises a mixture of organic and inorganic compounds.
 15. Theoptically clear biofouling resistant organosiloxane-based coatingcomposition for marine instrument housings and sensors of claim 14,wherein the adhesion promoter comprises greater than 60.0 wt %Octamethyltrisiloxane, 5.0-10.0 wt % 1-methoxyisopropyl orthosilicate,5.0-10.0 tetrapropyl orthosilicate, and 3.0-7.0 tetrabutyl titanate. 16.The optically clear biofouling resistant organosiloxane-based coatingcomposition for marine instrument housings and sensors of claim 1,wherein the composition further comprises at least one organic compoundhaving antibiofoulant properties selected from compounds consisting ofalgaecides, herbicides, bactericides, pesticides, capsaicin and zostericacid.
 17. A method of forming optically clear biofouling resistantcoating on marine instrument housings and sensors, comprising coating asurface thereof with a biofouling resistant composition comprising acurably reactive organopolysiloxane having at least one terminalreactive functional group and silicon bonded organic groups, anorganopolysiloxane cross linking agent, optionally a filler and/or areinforcing silica, optionally an adhesion promoter, and optionally ametal catalyst; wherein said terminal reactive group is a hydroxylgroup, an alkoxy group, an aryloxy group, an amino group, an amidogroup, a halogen, or a vinyl group; and said silicon bonded organicgroup is a methyl group, an ethyl group, a vinyl group, a haloalkylgroup, or a phenyl group; said coating composition having a refractiveindex of at least 1.30.
 18. The method of claim 17, wherein the curablyreactive organopolysiloxane of the biofouling resistant composition is ahydroxyl, alkoxy, aryloxy, amino, amido, halogen, or vinyl groupterminated polydimethylsiloxane.
 19. The method of claim 17, wherein thefiller comprises nanoparticles of amorphous fumed silica untreated ortreated with silanes.
 20. The method of claim 19, wherein said amorphousfumed silica is treated with trimethylchlorosilane,hexamethyldisilazane, or low molecular weight organoalkoxysilane,organochlorosilane, organosilazane.
 21. The method of claim 17, whereinsaid filler is a resin filler comprising short chain silicone polymersthat are soluble in the biofouling resistant organosiloxane-basedcoating composition.
 22. The method of claim 17, wherein said biofoulingresistant composition further comprises optically clear ingredients suchas diluents, extenders, stabilizers, surfactants, and processing aidssuch as cyclic or linear polydiorganosiloxanes.
 23. The method of claim22, wherein said diluents include silicon short chain linear siloxanes,cyclic siloxanes, and organic solvents.
 24. The method of claim 17,wherein said biofouling resistant composition comprises about 40-70 wt %dimethyl, methylhydrogen siloxane; 15-40% dimethyl siloxane,dimethylvinyl-terminated; 10-30 wt % dimethylvinylated and trimethylatedsilica; 1.0-5.0 tetramethyl tetravinyl cyclotetrasiloxane; less than 1wt % ethylbenzene, 0.5 wt % xylene, and a catalytic amount of platinum.25. The method of claim 17, wherein said biofouling resistantcomposition comprises about 60-90 wt % vinylpolydimenthylsiloxane;10-30% vinyl containing resin (ployalkylalkenylsiloxane); 0.0001benzene; 0.0001 toluene and a catalytic amount of platinum.
 26. Themethod of claim 17, wherein said biofouling resistant compositioncomprises about 60-80 wt % dimethylsiloxane, hydroxy-terminated;7.0-13.0 wt % amorphous fumed silica; 1.0-5.0 wt %ethyltriacetoxysilane; 1.0-5.0Wt % methyltriacetoxysilane.
 27. Themethod of claim 26, wherein said biofouling resistant compositionfurther comprises at least one of tetramethoxysilane, tetraethoxysilane,dimethyldimethoxysilane, methylphenyldimethoxysilane,methylphenyldiethoxysilane, phenyltrimethoxysilane,methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane,allyltrimethoxysilane, allyltriethoxysilane, or other alkoxysilanes. 28.The method of claim 17, wherein said adhesion promoter is at least onesilane coupling agent selected from the group consisting of3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyl trimethoxysilane,3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, a condensationreaction product between 3-glycidoxypropyltrialkoxysilane and asilanol-endcapped dimethyloligosiloxane, a condensation reaction productbetween 3-glycidoxypropyltrialkoxysilane and a silanol-endcappedmethylvinyloligosiloxane, condensation reaction product between3-glycidoxypropyltrialkoxysilane and a silanol-endcappeddimethylsiloxane-methylvinylsiloxane copolymer.
 29. The method of claim17, wherein said adhesion promoter comprises a mixture of organic andinorganic compounds.
 30. The method of claim 29, wherein said adhesionpromoter comprises about 60.0-85.0 wt % Octamethyltrisiloxane, 5.0-10.0wt % 1-methoxyisopropyl orthosilicate, 5.0-10.0 tetrapropylorthosilicate, and 3.0-7.0 tetrabutyl titanate.
 31. The method of claim17, wherein said biofouling resistant coating composition furthercomprises at least one organic compound having antibiofoulant propertiesselected from compounds consisting of algaecides, herbicides,bactericides, pesticides, capsaicin and zosteric acid.
 32. The method ofclaim 17, wherein the sensor elements is made of stainless steel, glass,epoxy, polyurethane, titanium, ceramics polyvinylchlorides (PVC),polycarbonates (PC), polyurethanes (PU), polypropylenes (PP),polyethylenes (PE), polyesters, polymethylmethacrylate (PMMA),hydroxyethylmethacrylate, N-vinyl pyrrolidones, fluorinated polymerssuch as polytetrafluoroethylene, polyamides, polystyrenes, copolymers ormixtures of the above polymers.
 33. The method of claim 17, wherein thehousing element is made of aluminum, titanium, stainless steel, coppernickel, glass, polyurethane, poly vinyl chloride, ceramic, poly acetyl,fiberglass reinforced plastic, carbon fiber reinforced plastic, otherthermo plastics, other thermo sets.
 34. The method of claim 17, whereinthe marine instrument is an acoustic sensor, optical sensors electrodeor electromagnetic sensors strain gauge devices.
 35. A method ofpreventing or reducing biofouling on marine instrument housings andsensors comprising using mechanical wipers on surfaces coated with anoptically clear biofouling resistant coating composition comprising acurably reactive organopolysiloxane having at least one terminalreactive functional group and silicon bonded organic groups, anorganopolysiloxane cross linking agent, optionally a filler and/or areinforcing silica, optionally an adhesion promoter, and optionally ametal catalyst; wherein said terminal reactive group is a hydroxylgroup, an alkoxy group, an aryloxy group, an amino group, an amidogroup, a halogen, or a vinyl group; and said silicon bonded organicgroup is a methyl group, an ethyl group, a vinyl group, a haloalkylgroup, or a phenyl group.
 36. A method of forming durable opticallyclear biofouling resistant coating on marine instrument housings andsensors, comprising first coating a surface thereof with an opticallyclear tie coat, and then coating said surface with a biofoulingresistant composition comprising a curably reactive organopolysiloxanehaving at least one terminal reactive functional group and siliconbonded organic groups, an organopolysiloxane cross linking agent,optionally a filler and/or a reinforcing silica, optionally an adhesionpromoter, and optionally a metal catalyst; wherein said terminalreactive group is a hydroxyl group, an alkoxy group, an aryloxy group,an amino group, an amido group, a halogen, or a vinyl group; and saidsilicon bonded organic group is a methyl group, an ethyl group, a vinylgroup, a haloalkyl group, or a phenyl group.
 37. The method of claim 36,wherein the tie coat is a primer capable of forming an intimate covalentbond matrix with the instrument housing and/or sensor surface.
 38. Themethod of claim 36, wherein the tie coat is a polyamine/polyamide blendepoxy resin comprising about 65-70 Wt % Bisphenol a-epichlorohydrinpolymer; 30-35 wt % Alkyl(c12-14) glycidyl ether; diluent n-Butylglycidyl ether; and C18-unsaturated fatty acids, dimers, and reactionproducts with polyethylenepolyamines.
 39. The method of claim 36,wherein the tie coat is an epoxy resin comprising about 25-50%;polyoxypropylenediamine; reaction products of isophorone diamine withphenol/formaldehyde 10-25%; Isophoronediamine 10-25%; Reaction productsof benzene-1,3-dimethanamine with hydroxybenzene and formaldehyde10-25%; Hydroxybenzene 5-12% and m-Xylene diamine 5-12%.
 40. The methodof claim 36, wherein the tie coat is an epoxy resin comprisingBisphenol-A type epoxy resin 50-70%; Benzyl alcohol 10-20% Bisphenol-Ftype epoxy resin 10-20%; Ethylene glycol monobutyl ether 0.1-0.3%. 41.The method of claim 36, wherein the tie coat is a polyurethane adhesive.42. The method of claim 36, where in the surface to be coated is coronatreated.
 43. A method of forming durable optically clear biofoulingresistant coating on marine instrument housings having one or moresections in O-ring sealable engagement comprising the steps of: a)putting a clear plastic tape over the O-ring sealable engagement; b)coating the clear plastic tape with the biofouling resistant coatingcomposition of the present invention; c) forming at least one hole onthe tape in order to equalize the pressure across the tape.